Alfalfa at both the SUNY Cobleskill Farm and the Cornell Research Farm in Valatie were 18 to 20 inches tall. There was a range of 1st to 3rd instar alfalfa weevil larvae at the SUNY Cobleskill farm, while I did not find any larvae at the Valatie research farm. It is a bit odd because the Valatie site is normally ahead of the Cobleskill site in alfalfa weevil development. I did find substantial numbers of adult alfalfa weevil at the research farm. Other insect pests I found were clover root curculio, tarnished plant bug and clover stem weevil. Clover stem weevil (Ischnopterapion virens) is a tiny blue weevil and a pest of clover. This weevil is native to Europe and is relatively new to the
United States. Adults are metallic blue, about 3/16 inches long, with a distinctive snout and straight antennae. Adults make small circular holes in leaves of white clover. Larvae tunnel in the runners of white clover and stems of red clover. The economic damage status of this weevil is not known. Here is a photo of this insect:

Clover stem weevil

I found symptoms of spring black stem under the canopy of alfalfa at the SUNY Cobleskill farm. This disease is very common to find in alfalfa fields in NYS. Spring black stem is favored by cool and moist weather in early spring. Symptoms appear as irregularly shaped brown to black spots that can merge to form a larger blotch. This disease can infect the petiole, form elongated blackened areas on the stems, and may be a contributor to crown rot.

Tom Kilcers triticale trials looked good this week and there was only a little disease (Septoria tritici or Stagonospora nodorum blotch) on the very lower leaves. I also scouted grass hay fields at the SUNY Cobleskill farm this week looking for possible armyworm larvae since to the south populations have been very high. I did not find any small larvae but will continue to look at these grass hay fields in the weeks to come. Last week, I stated that I would have an article on insect pests of canola. I will have this article prepared for you next week. Sorry about the delay!

Western NYS-Julie Dennis

Mike Stanyard, NWNY Team, reports that powdery mildew in the spore stage is common in wheat fields, even on flag leaves. The disease is not typically uniform throughout fields.

Rainfall was above normal along the Southern Tier, southern
HudsonValley, Catskills, Coastal region and the St. Lawrence Valley. Several locations in these areas had over an inch of rainfall. The Northern Plateau,
MohawkValley, Great Lakes,
CentralLakes, and upper
HudsonValley averaged below normal with totals in the 0.13 to 0.6 range.

There were fewer than 25 (base 50) GDD days during the period May 15-21 which put the seasonal total in the 100 to 300 range across much of the state. At this point in the growing season the base 50 GDD accumulation is very close to the 30 year average, but lags the accumulation we saw at this time last year by as much as a week in the eastern part of the state. The accumulation is slightly ahead of last year in the far west.

Forecast

Unseasonably cool and showery weather will persist through today. Conditions will improve through the weekend, as the upper level low that has sat over the Northeast finally moves out of the area. A ridge of high pressure will build into the region bringing a return to sunshine and a warming trend by the weekend and into early next week. Clearing on Friday will introduce the potential for frost in some areas Friday night into Saturday morning. Temperatures will warm up to above normal by Monday, with highs on Monday exceeding 80 in parts of the state. A cold front is expected to traverse the state Monday evening into Tuesday with a chance of showers and a cool down. High pressure will build again for Tuesday and Wednesday bringing near normal temperatures (highs in the 70s lows in the low 50s).

The longer term outlook (next Wednesday through June 3) is for near or slightly below normal temperatures and below normal precipitation.

Alfalfa weevil larvae have been seen in several locations over the past couple of weeks, but widespread damage is not being reported yet. Biological control agents are a significant reason that alfalfa weevil (AW) often remains well below economic thresholds in NY.

Within 10 years of the arrival of the invasive alfalfa weevil in the
US in the late 1940s, USDA scientists began releases of parasitic wasps to combat this devastating pest. A parasitic wasp lays an egg in an AW larva, thus killing the larva of the pest insect and providing the food source for a growing parasitic wasp. How do we know if these wasps are helping us out in our fields? One of the revealing times to look for alfalfa weevil parasitoids is when they are in the pupal stage. Based on growing degree day accumulations so far this season, the pupal stage is still a ways in the future. Check out the AW GDD map later in this report to track GDD accumulations in your area of NY.

While searching for alfalfa weevil pupae later this month or in early June, keep your eyes out for the parasitoid pupae, too. Alfalfa weevil pupae can be found inside small net-like, pea-sized cocoons generally found in lower regions of the plant on or 2-3 inches above the soil surface. The alfalfa weevil pupa is surrounded in a white to tan webbing, often associated with a leaf, and a wasp pupa is instead surrounded by a small hard brown capsule-shaped pupal case (see photos). Enclosed in the brown case is the wasp pupa, which has grown up using the alfalfa weevil larva as its food source.

Alfalfa weevil pupae

Pupae (within their cocoons) of parasitic wasps of Alfalfa Weevil

The two most common parasitic wasps of AW in NY are in the genus Bathyplectes. Their pupae are enclosed within the mahogany colored shells, or cocoons, with white bands (2nd and 3rd from the left in the above photograph). These two parasitoid species tend to lay eggs in the early alfalfa weevil larval stages. Only a single parasitoid can successfully develop in a host weevil larva. The two species can be distinguished from each other as pupae. Batheplectes anurus has a raised white band and the cocoon has the unusual habit of jumping when disturbed. B. curculionis does not have a raised white band, and the cocoons do not jump.

There have been reports of very high levels of true armyworm in the
Southern US. The
University of
Kentucky reports the highest ever capture of armyworm moths. While trapping does not indicate damage to a field it does tell us potential infestation levels. We have not has any significant storms to bring this insect pest North yet this year. The potential still exists and we could receive them as we start to get weather fronts from the southwest of NY. Keep a close eye on small grains, pasture, grass hay, and corn.

True armyworm larvae appear smooth, cylindrical, and pale green to brownish when they are still small. Mature larvae are smooth and marked with two orange, white-bordered strips on each side. True armyworm ranges in size from 1/8 inch to 1.5 inches long. There is a website with a photo of armyworm: Armyworm photo

It is important to detect areas of armyworm infestation early, while larvae are still small, since large larvae do most of the feeding and quickly destroy whole stands of corn, grasses and small grains. Because armyworm feeds at night look for chewed leaves, cut stems, lodged plants, pellet-like frass on the ground, and larvae hidden under plant canopy and surface residue. You will need to be aware that armyworms can move from field to field very quickly. Start scouting for the armyworms in May and repeat scouting every 3 days to 5 days. Monitor fields for armyworm larvae when they are less than 1/2 inch long. If there are sufficient numbers and damage is present, an insecticide could be justified. Treat only the affected area and a 20 to 40-foot border around the infestation. Rarely does a whole field need to be treated for armyworm. Larger armyworm larvae, greater than 1/2 inch long, are much more difficult to control. These large larvae are more tolerant of insecticides, reducing the effectiveness and economic viability of this option.

Will Conditions be Favorable for Fusarium Head Blight (Scab) This Year?

One of the most devastating diseases of wheat is Fusarium head blight, or scab. The disease reduces yield by decreasing the number of viable kernels, but the more significant impact is that the fungus in diseased kernels may produce DON, a mycotoxin called deoxynivalenol (DON). DON is sometimes called vomitoxin because of the impact on the digestive system of swine and other animals with simple stomachs. The rejection of infected grain by buyers is the most significant cause for wheat losses to Fusarium head blight.

Scab is caused by airborne spores of the fungus Fusarium graminearum that dwell in nearby or distant crop debris, including corn stalks and wheat straw. This is the same fungus that can cause root, stalk, and ear rots of corn. Since the fungus is very widespread, likelihood of exposure is not reduced sufficiently by crop rotation or other cultural practices. Extended periods of warm, moist weather at crop flowering can cause the florets to be infected just after anther emergence, killing the florets and preventing kernels from developing. Symptoms of scab become visible on emerged heads within weeks after flowering. During early grain fill, the disease shows up as pink to salmon orange on infected kernels. As kernel fill progresses, the infected kernels appear bleached.

Gary Bergstrom tells us that this model mainly predicts the likelihood of spore build-up based on temperatures and rainfall amounts prior to wheat flowering. Using the new 24-48 hour forecast weather feature of the model, one can also get an idea of the favorability for actual infection. It shows us a ball-park of areas to focus our scouting efforts. Unfortunately, the model does not accurately predict the level of toxin contamination in grain, particularly if there is a sustained rainy spell during grain-fill.

New in our arsenal this season is the availability of Tilt fungicide that provides fair control of scab. Please refer to the table in the article at this link for specific recommendations on wheat fungicides: Wheat Fungicides Options for 2008.

It is important to note that strobilurin fungicides have actually been shown to increase vomitoxin occurrence when applied at heading!

Plant pathologists and plant breeders continue the active development of varieties resistant to Fusarium head blight. Newly released this year is the Cornell variety called Jensen, developed by Mark Sorrells, Cornell Department of Plant Breeding. Jensen has shown more resistance to fusarium head blight (scab) than other white wheat varieties typically planted in NY.

Rust continues to be found in the southern U.S. Active disease is still being reported on kudzu in six counties in
Florida and one county in
Texas. Efforts continue in the Gulf Coast Region to establish soybean rust sentinel plots.

Coordination of soybean rust sentinel plots in
New YorkState is currently underway. Many of last years cooperators will be volunteering their time again to establish and scout these plots. Please visit us again for future updates.(Updated May 14, 2008 )

If you are unable to reach a Poison Control Center or obtain the information your doctor needs, the office of the NYS Pesticide Coordinator at Cornell University, 607-255-1866, may be able to assist you in obtaining such information.

NYS IPM on:

These pages are maintained by the New York State IPM Program, part of Cornell Cooperative Extension. All material is protected by Section 107 of the 1976 copyright law. Copyright is held by Cornell University and the New York State IPM Program.